Cosmology

Cosmologyis a branch of astronomy and of metaphysics committed to the study of the universe as a whole, of the contents, structure, and evolution of the universe from the beginning of time to the future.

As a branch of two very old endeavours of humanity, the study of the sky and the origins of the world, it embraces numerous related inquiries concerned with the world we live in and, to the extent it could be imagined and observed, the universe. As a branch of metaphysics it attained some prominence when Christian von Wolffe published Discursus Praeliminaris de Philosophia in Genere (1728). Von Wolff placed cosmology in his classification scheme of the main areas of philosophy, distinguishing cosmology from ontology, theology and psychology, essentially making it a distinctive field of philosophy unto itself. As a philosphy, its nature has been disputed over time since von Wolff but it can be said that generally, it is thought to encompass humanity's experience in, and the nature of, the physical world. As a science, it encompasses the work of observational astronomy and theoretical physics as scholars in both fields attempt to describe and explain the physical universe. Cosmology, as a science, attempts to construct models of the physical universe from observational data which are then tested. Cosmology, as metaphysics, involves a priori investigations of a rational cosmology and the conceptual and categorical analyses of the speculative philosopher.

Ancient cosmology

Any attempt to understand cosmology, or simply what humanity thought about the universe whenever that might have occurred to them prior to the last few millennium would be largely guess work. Their understanding would have been inextricably interwoven with their impressions and their imagination. Impressions would have been made in a facile manner, what ever they could see where ever they were, their immediate circumstance, their fears and attempts at explaining the mysterious, all would have come together in a variety of concepts about the nature of the universe.

What we consider cosmology today, if we are addressing explanations from observations and precise measurements that can be duplicated--the scientific approach--or at least its basic and most primitive roots, it would have been fraught with almost anything but what we consider scientific. Simple deduction about how fire is made and food accessed and shelter constructed would have been within the reach of prehistoric and ancient humanity, but how close they came to an understanding, no matter how fragmented or trivial, of the universe as we know it today, is simply beyond us to ever know. That they observed that things seemed to be regular and predictable is evident from stone circles and other constructions that indicated they knew the sun would strike a certain point on the ground at a certain time every year, the moon would change appearance on a regular basis--any number of possible conclusions could be reached about these clues that have been left. Burial customs going back as far as the last twenty millennium might indicate a belief in the after life, possibly an eternal existence—but that too is reaching and can not be safely concluded.

Since prehistoric people left only fragments of their impressions in relics and documents and instruments of most ancient sources have long since disappeared, prehistoric and ancient humanity's understanding will always be a fragmented picture to us today. In fact, if the definition of cosmology would be constructed around what it was meant to achieve, if it was meant to explain things, it would not necessarily follow that those explanations would be tested as we expect scientific theories to be tested today. The result of such explanations would be extraordinary people, monsters, places and events which would not be verifiable, such as monsters at the edge of the world as mariners sometimes believed as late as the 15th century.

The first solid evidence of a cosmological model that would explain observations come to us from the Greeks of the 4th century B.C.. Babylonians in the 4th millennium B.C. were making accurate observations of the planets, the moon, the stars and the Sun and were providing reasonable predictions of their motions, but they did not leave us with a model to explain these motions as the Greeks did.

The Greeks over time developed a cosmological perspective that the stars were placed firmly and unchangingly in the sky in a sphere that rotated around the Earth every 24 hours. Likewise, the planets, the Sun and the Moon, everything not on the Earth moved in a zone of aether between the Earth and the stars.

This model had many contributors and some detractors, unfortunately the records of their thoughts and work are often fragmentary at best and some we know of only through the comments of others. By the second century, Ptolemy of Alexandria (he may have been Egyptian or he may have been Greek) set down a system to account for the motion of the planets and the Sun and the Moon and the stars around the Earth, a model that was based on perfect circles and epicycles to explain loops observed in planetary motions, loops that were actually retrograde motion caused by the motion of the Earth's movement around the Sun along with the other planets. It was a very complicated system and it stood for a long time. Its demise was posited by quite a number of people over the centuries, even before Ptolemy. but it was not seriously rejected until Galileo. Even the concept of aether lasted until the late 19th century when the Michelson-Morley Experiment failed to account for the aether wind.

Medieval cosmology

The Medieval period is generally cast as that time when the Roman Empire withdrew from the West and the coming of the Renaissance, a period of approximately 476 to 1453 A.D. In this period the work of Ptolemy held sway, the universe was geocentric, it moved about the Earth which was the center of the universe.

Modern Cosmology

A seminal project in the advancement of cosmology was COBE. With COBE, the extent and precision of the data gathered shifted the entire field of cosmology prompting the Nobel Foundation (Royal Swedish Academy of Sciences) to comment, "the COBE-project can also be regarded as the starting point for cosmology as a precision science: For the first time cosmological calculations (like those concerning the relationship between dark matter and ordinary, visible matter) could be compared with data from real measurements. This makes modern cosmology a true science (rather than a kind of philosophical speculation, like earlier cosmology)."

Leading theoretical focus

The Big Bang

The Big Bang, a label bestowed derisively by its leading critic, Fred Hoyle in the early part of the 20th century, is basically a theory of the universe with a beginning, and possibly an end. Until the Big Bang, cosmology was established on an immutable, everlasting and unchanging universe, the Aristotelian model.

Until Georges Lemaître, the idea of a beginning was hotly rejected, even by those whose evidence best supported this theory, people such as Einstein and Hubble.

In essence the Big Bang is about a moment--an extremely short moment--wherein all the matter and energy of the universe is condensed into a space smaller than the subatomic components of an atom, and then are released in a sudden moment. The problem with this model of the cosmos is that prior to the moment of the Big Bang, it is not possible to actually investigate what happened, to scientifically research the nature of things, a problem that nearly lead Einstein to ultimately reject this theory.